<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>

<body>
  <script>
    let years = parseFloat(prompt("请输入年份："));
    if (((years % 4 === 0) || (years % 400 === 0)) && (years % 100 !== 0)) {
      alert("闰年");
    } else {
      alert("不是闰年");
    }
  </script>
</body>

</html>